Use a fishbone to identify potential causes of an effect. A fishbone is also called a cause-and-effect (C&E) diagram or an Ishikawa diagram.

On a fishbone, the effect, or central problem, is on the far right. Affinities, which are categories of causes, branch from the spine of the effect. Causes branch from the affinities. By default, affinities and causes are expanded so that you can view all levels of the fishbone.

Example of a fishbone

This fishbone identifies the potential causes of delayed lab results.

Answers the questions:
  • What are the potential causes for a particular type of defect?
  • What are the process inputs that contribute to variation in the process output?
When to Use Purpose
Pre-project Assist in project identification by linking potential causes to defects.
Start of project Assist in problem identification.
Mid-project Identify potential process inputs to investigate in the project to determine which inputs have a significant influence on the process output.

Data

This tool has no data requirements because you use it only to collect and organize data.

Guidelines

  • Be sure to include project stakeholders in the brainstorming sessions for building the fishbone diagram.
  • If the standard categories of the causes are not appropriate for the problem, create new ones. For example, service-quality applications often include personnel, procedures, and policies. However, fishbone diagrams can include any type of cause you want to investigate.

How-to

  • Gather the project team and appropriate stakeholders for a brainstorming session.
  • Determine the primary categories (affinities) for the causes of the problem (for example, personnel, machines, methods, materials, measurements, and environment).
  • For each primary category, list all possible causes or process inputs. You may want to establish secondary categories for some or all of the primary categories, then list the causes or process inputs under the secondary categories.
  • Highlight causes (or inputs) that are deemed to be the most important by the team.
  • Record the categories and causes, using the fishbone tool.

For more information, go to Generate a brainstorm list.

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